x86: use static_cpu_has in uaccess region to avoid instrumentation

This patch is a pre-requisite for enabling KASAN bitops instrumentation;
using static_cpu_has instead of boot_cpu_has avoids instrumentation of
test_bit inside the uaccess region.  With instrumentation, the KASAN
check would otherwise be flagged by objtool.

For consistency, kernel/signal.c was changed to mirror this change,
however, is never instrumented with KASAN (currently unsupported under
x86 32bit).

Link: http://lkml.kernel.org/r/20190613125950.197667-3-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>